In a turbomachine, the stator nozzles that are exposed to high temperatures, in particular those downstream from the combustion chamber, include internal cavities for passing a flow of cooling air coming from a radially outer enclosure, part of which air can be diffused into the passage for passing the flow of combustion gas via holes formed in the vanes, and part of it can be exhausted into a radially inner enclosure.
Link means are provided between these enclosures and the stator nozzles to allow cooling air to pass, while minimizing losses and leaks at the interfaces, the link means comprising metal tubes having their ends mounted in leaktight manner in orifices in a casing and in orifices in the stator nozzles.
While the turbomachine is in operation, the casing, and above all the stator nozzles, expand thermally and are subjected to high levels of vibration, thereby generating relative displacements and changes in alignment between the orifices in the casing and those in the nozzles.
To compensate for these relative displacements and changes in alignment, link tubes are used having ends that are enlarged in such a manner as to allow for a small amount of pivoting of the ends of the tubes in the orifices in the casing and in the nozzles, these ends being mounted as tight-fits in the orifices in order to ensure that the assembly is sufficiently leaktight.
Nevertheless, that solution is not satisfactory insofar as mounting the ends of the tubes as tight-fits limits the extent to which they can pivot and leads to zones that present high degrees of wear due to friction against the inside surfaces of the orifices in the casing and in the nozzles, which can lead to leaks at said ends, and even to the link tubes being lost or failing.
According to European patent EP-A2-1 164 250, one solution to this problem consists in associating a ring with each link tube, the ring being mounted between one of the ends of the tube and a nozzle, and carrying an outer collar that can be moved in sliding between a surface of the nozzle and a surface of an annular element fitted on the nozzle and held stationary relative thereto.
Nevertheless, that solution is unsatisfactory since it does not make it possible to compensate relative displacements in rotation between the casing and the nozzle without leading to high degrees of wear in the link tube.